What is compaction? Why is it needed?

What is compaction? 

Why is it needed? 

List the different methods of compaction.

Compaction

 It is a process in which the soil particles are brought close to each other due to expulsion of air from the voids present in the soil on application of an eternal stress. Thus the volume change I the soil is brought about by removal of air from the soil. It is almost an instantaneous process.

Need for compaction

 Compaction, in general, increases the shear strength of soil due to closer arrangement of soil particles. This in turn increases the stability and bearing capacity of soil.

Different methods of compaction

(i) Rollers: 
Various types of rollers are used for compaction of soil. The selection of a particular type of roller depends on the contact pressure required; thickness of soil layer, number of passes required, speed of roller etc. rollers may be smooth wheeled, pneumatic tyred or sheep foot rollers.

(ii) Tampers:
 Tamper (or rammer) is a block of iron about 3 to 5 kg in mass which is attached to a wooden/steel rod. The tamper is usually lifted to about 300 mm and dropped freely on to the soil thereby compacting the soil. Mechanical or machine operated rammers are muchheavier (around 30 to 150 kg) and are also dropped from a larger height.

(iii) Vibrators :
 Vibrators or vibratory rollers bring about the compaction of soil by transmitting vibrations to the soil. Vibratory rollers are particularly useful for compacting sandy soils.








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